From 288380d4578e6e0be913fea6852226227a6c4170 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20K=C3=A5re=20Alsaker?= <john.kare.alsaker@gmail.com>
Date: Sat, 9 Mar 2024 01:26:59 +0100
Subject: [PATCH] Lock stderr in panic handler

---
 compiler/rustc_driver_impl/src/lib.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/compiler/rustc_driver_impl/src/lib.rs b/compiler/rustc_driver_impl/src/lib.rs
index e06d1d245b23f..b748190718772 100644
--- a/compiler/rustc_driver_impl/src/lib.rs
+++ b/compiler/rustc_driver_impl/src/lib.rs
@@ -1317,6 +1317,9 @@ pub fn install_ice_hook(
     panic::update_hook(Box::new(
         move |default_hook: &(dyn Fn(&PanicInfo<'_>) + Send + Sync + 'static),
               info: &PanicInfo<'_>| {
+            // Lock stderr to prevent interleaving of concurrent panics.
+            let _guard = io::stderr().lock();
+
             // If the error was caused by a broken pipe then this is not a bug.
             // Write the error and return immediately. See #98700.
             #[cfg(windows)]